"The other thing that made the process interesting and difficult is that occasionally – maybe once or twice per episode – there would be a telesnap that didn’t correspond to the camera script, because the camera script only describes the plan of action for a recording, and not what was actually shot, and so inevitably the plan would change during the camera rehearsals as the director found that he needed a different shot to tell the story, or had to use a different camera for one shot because the camera he’d planned to use couldn’t move from another set soon enough or would get its cables tangled up or whatever. So whilst the camera scripts are generally very accurate, they’re not the whole story; if you compare an existing episode to its camera script you’ll notice numerous small differences between the plan and the realisation, usually in terms of the timing of cuts."

The appearance of these specials is a coincidental godsend as my rewatch of the whole of Who is just about reaching the moment when what's available becomes decidedly patchy.